The present invention relates to an intra aural probe for monitoring multiple physiological parameters simultaneously. In particular, the intra aural probe, which comprises a pressure sensor, a temperature sensor and a light sensor, is configured to fit snugly and sealinily within the outer aural cavity. Physiological parameters which can be monitored by the intra aural probe of the present invention include blood pressure, pulse rate, and volume of blood, respiratory rate and respiratory volume.
There are certain parameters of human physiology that are of great importance for monitoring the well being of a person in many situations. These are; heart rate, blood pressure, respiratory rate, respiratory volume, core temperature and the blood oxygen content sometimes referred to as pulse oximetry. The heart rate is the number of beats per minute and can be measured by counting the pulse at the wrist but is most commonly measured using electrocardiography. This requires electrodes to be placed evenly on three limbs or adjacent portions of the torso. The electrodes cause skin irritation and are subject to electrical noise.
The blood pressure cycles up and down as the heart beats. It is recorded as systolic (upper) and diastolic (lower) pressures during the cycle. Until the development of this method it could only be measured accurately by placing a pressure transducer directly into the artery. An approximate measure could be obtained by placing a semi-inflated cuff around the finger and measuring the added pressure as blood moved into the finger. The latter method is particularly inaccurate when the blood flow to the finger is decreased by cooling the periphery or disease states. An intermittent measurement can be made by inflating a cuff on the upper part of the limb and recording the pressure required to occlude the blood flow in the vessels below. It can not provide a continuous measure. A variant referred to as pulse pressure is the difference between the upper systolic and lower diastolic pressures and can be represented both as a numerical value or a waveform moving from one to the other.
Respiratory rate is the number of breaths per minute and can be measured by counting the expansion and contraction of the chest. It can be monitored continuously using impedance plethysmography, where electrical resistance changes with the volume of the chest. It requires electrodes to be placed on two limbs or either side of the chest. The respiratory volume is the amount of air moved in and out during a breath. The shape of the movement is also valuable information. It can be approximated using the impedance plethysmography but otherwise can only be accurately measured by breathing through a tube into a volume measuring device.
The blood oxygen content is usually measured by infra red spectroscopy. Based on the observation that blood goes from blue to red as it picks up oxygen, the percentage of red blood cell haemoglobin carrying oxygen is calculated from the absorption of different coloured light. The technology is well established in many monitoring situations and is now obligatory during general anaesthesia in most countries. The probe itself is usually applied to the finger but can be clipped to an ear lobe.
Core temperature is a measure of the body""s temperature on the central portion such as the heart and brain. Temperature measurements taken in the mouth or axilla are routinely lower and less reliable. During certain situations such as severe dehydration core temperature can increase even when the peripheral temperature does not because of the decreased blood flow to the periphery. Traditionally such core temperature measurement can only be made intermittently using an infra red system applied to the external ear or continuously by placing a temperature probe in the anus.
The technology used in present day modern care facilities requires different measurement systems to be applied to different positions on the body or by the use of very invasive medical devices such as intra arterial catheters and intratracheal tubes. Often these technologies get in the way of the surgeon performing a procedure and severely limit patient mobility and comfort. In certain situations such as monitoring a fighter pilot or a patient during transport, these systems are detrimentally effected by the movement and vibration or simply can not be applied.
In addition, these devices are trying to measure the state of oxygen delivery to the brain, the organ most sensitive to loss of blood flow or oxygenation of the blood. The technology presently used does not measure the supply going to the brain itself and therefore can at best make assumptions based on the activity of the heart and lung and the blood oxygen in other vessels.